The DG419looks into the high input impedance of the op amp, so the effects of Rvs(o`l are negligible. The DG441 is also connected in series with RIN and is not included in the feedback dividers, thus contributing negligible
Digitally-programmable-precision-amplifier - schematic

Because the DG419 and DG441 can handle ±15 V, the unity gain follower connection, Xl, is capable of the full op-amp output range of ± 12 V.